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jit.scalebias and jit.pack: no effect on alpha channel

November 28, 2010 | 3:29 am

Dear all,

On the Windows version of Jitter, there is no change to transparency when I manipulate the alpha channel of an image, whether I’m using jit.scalebias or jit.pack. This occurs whether I’m using a PNG, GIF or TIF file, and that includes files where I have made sure to add an alpha channel through GIMP.

An example is attached. I like using transparency, so any solutions would be greatly appreciated!

– Pasted Max Patch, click to expand. –

November 29, 2010 | 7:02 pm

alpha channel is generally only useful when compositing matrices.
you can use jit.alphablend to composite two matrices using the alpha channel of one of them.
here is a basic example. (the alpha channel is generated using the @planemap attribute, but you can replace that with your own images with an alpha channel and get the same results).

– Pasted Max Patch, click to expand. –

November 29, 2010 | 8:17 pm

Rob,

Thank you for this. I’ve had to realize that alphablend is apparently the only basic way of achieving transparency within Jitter. It’s still strange that while in image software you can change the opacity in a single step, working only on the alpha channel itself, resulting in anything behind the image showing through, in Jitter you have to match the background color and alphablend it into a jit.pwindow to get the same effect. The jit.pwindow object apparently does not support opacity between itself and what is behind it.

Hence my confusion.

Anyway, this trick will do. Thanks again.


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